1. Field of the Invention
The present invention relates to a robot coating system which includes a robot which is provided with a coating gun which uses a pump to coat a viscous material and by which the coating gun coats a plurality of planned coating positions on a workpiece with a viscous material in exactly predetermined amounts to thereby scatter coat the viscous material.
2. Description of the Related Art
An industrial robot, for example, a multiarticulated robot, which coats a viscous material includes a coating gun which is attached to the tip of the robot arm. The coating gun is provided with a pump. If driving the pump, the nozzle of the coating gun discharges a viscous material, for example, a paint or sealing material (see Japanese Patent No. 3961820 and Japanese Patent No. 3522329).
In coating work which coats a viscous material, it is necessary to define the start and end positions. A first method provides a robot teaching program in which a coating start position and a coating end position are defined. This method is used for coating work which coats a viscous material by a straight continuous path.
In a second method, a robot is made to temporarily stop at a target position, then the viscous material starts to be coated. Further, when predetermined coating work is completed with a designated coating time and coating speed or coating amount, the robot is made to move to the next target position where the above-mentioned coating work is again performed. This is frequently used in the case of scatter coating which repeatedly coats a plurality of target positions with fixed coating amounts.
In both the above-mentioned first and second methods, when some sort of abnormality occurs at the robot at the time of the robot coating work and an alarm is issued and the robot stopped, the coating gun simultaneously stops. In this case, the coating gun stops before discharging the intended coating amount.
In this connection, the first method designates a coating start position and a coating end position. This is suitable for coating work which coats a viscous material without interruption on a continuous path. However, in the first method, the time which is required from the coating start to coating end is determined in accordance with the content of operation of the robot. Obtaining the time uniquely is extremely difficult.
Further, the amount of coating of the viscous material at the coating gun is determined in accordance with the coating speed, coating time, internal pressure of the viscous material before coating (hereinafter referred to as the “pilot pressure”), etc. Therefore, if using the first method for scatter coating, the coating time is not uniquely determined, so a fixed amount of coating cannot be obtained. Therefore, when coating a sealing material, there is a possibility of variation occurring in the sealing strength. Furthermore, when the coating gun stops, the coating work is interrupted, then the coating work is resumed, it is hard to make the sum of the amount of coating before resumption of the coating work and the amount of coating after resumption strictly match with the intended amount of coating.
Furthermore, in the second method as well, there is a similar problem when the coating gun is stopped, the coating work is interrupted, then the coating work is resumed. In the second method, it is necessary to make the robot stop temporarily at the target position in the coating work, so there is the problem that the cycle time of the robot system increases.
The present invention was made in consideration of this situation and has as its object to provide a robot coating system wherein the amount of coating of the viscous material does not change from the intended coating amount even if the coating work is interrupted and then the coating work is resumed.